Re: [PATCH] iio: light: vcnl4000: Fix WARN_ON on uninitialized lock

[Jonathan Cameron <Jonathan.Cameron@huawei.com>]

On Mon, 30 Jan 2023 15:10:40 +0100
Mårten Lindahl <martenli@axis.com> wrote:

> On 1/30/23 14:04, Jonathan Cameron wrote:
> > On Mon, 30 Jan 2023 10:37:42 +0100
> > Mårten Lindahl <marten.lindahl@axis.com> wrote:
> >  
> >> There are different init functions for the sensors in this driver in
> >> which only one initialize the generic vcnl4000_lock. With commit
> >> e21b5b1f2 ("iio: light: vcnl4000: Preserve conf bits when toggle power")
> >> the vcnl4040 sensor started to depend on the lock, but it was missed to
> >> initialize it in vcnl4040's init function. This has not been visible
> >> until we run lockdep on it:
> >>
> >>    DEBUG_LOCKS_WARN_ON(lock->magic != lock)
> >>    WARNING: CPU: 1 PID: 8800 at kernel/locking/mutex.c:575 __mutex_lock+0x4f8/0x890
> >>    ...
> >>    Call trace:
> >>     __mutex_lock
> >>     mutex_lock_nested
> >>     vcnl4200_set_power_state
> >>     vcnl4200_init
> >>     vcnl4000_probe
> >>     i2c_device_probe
> >>     really_probe
> >>     __driver_probe_device
> >>     driver_probe_device
> >>     __driver_attach
> >>     bus_for_each_dev
> >>     driver_attach
> >>     bus_add_driver
> >>     driver_register
> >>     i2c_register_driver
> >>     vcnl4000_driver_init
> >>     do_one_initcall
> >>     do_init_module
> >>     load_module
> >>     __do_sys_finit_module
> >>     ...
> >>
> >> Fix this by adding mutex_init on the lock in the init function used for
> >> vcnl4040.
> >>
> >> Fixes: e21b5b1f2 ("iio: light: vcnl4000: Preserve conf bits when toggle power")
> >> Signed-off-by: Mårten Lindahl <marten.lindahl@axis.com>  
> > Perhaps better to pull the lock out of the device specific setup?  
> 
> Hi Jonathan!
> 
> Ok, having a
> 
> static DEFINE_MUTEX(vcnl4000_lock);
> 
No. Definitely don't do that.  We need one per device instance.

I just meant move the mutex_init() into the main probe function rather
than the chip specific init that is called from there.

> will make sure initializing it wont be forgotten for specific setups.
> 
> I'll test it.
> 
> Kind regards
> 
> Mårten
> 
> >  
> >> ---
> >>   drivers/iio/light/vcnl4000.c | 1 +
> >>   1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/iio/light/vcnl4000.c b/drivers/iio/light/vcnl4000.c
> >> index cc1a2062e76d..a8a9fc3b1a02 100644
> >> --- a/drivers/iio/light/vcnl4000.c
> >> +++ b/drivers/iio/light/vcnl4000.c
> >> @@ -316,6 +316,7 @@ static int vcnl4200_init(struct vcnl4000_data *data)
> >>   	}
> >>   	mutex_init(&data->vcnl4200_al.lock);
> >>   	mutex_init(&data->vcnl4200_ps.lock);
> >> +	mutex_init(&data->vcnl4000_lock);
> >>   
> >>   	ret = data->chip_spec->set_power_state(data, true);
> >>   	if (ret < 0)